A pharmaceutical dry heat sterilizer is used for sterilization by using hot and dry air to remove contaminants. This article discusses dry heat sterilizers, its cycle and common equipment configuration.
Pharmaceutical dry heat sterilizers use dry, hot air to achieve sterilization in the pharma industry, along with other processes such as Autocalves. The dry and heated air is blown into the chamber until the pharmaceutical dry heat sterilizer chamber reaches the required temperature. Temperature is maintained for a specific time to achieve sterility. Once, the specified time is completed, sterilization stops, and items can be off-loaded from the DHS.
A pharmaceutical dry heat sterilizer is used in the sterile manufacturing process to sterilize containers before filling products into them. High temperature in a DHS causes the Coagulation of proteins, causing a change in the basic structure of contaminants. The DHS uses a common temperature range of 160°C to 200°C.
The cycle of pharmaceutical dry heat sterilizer
The entire sterilization cycle of a pharmaceutical dry heat sterilizer is divided into a series of steps. Each step is necessary and has a definite part in the success of a sterilization process. It is also essential that each step must be completed in sequence. Otherwise, it will fail the sterilization process.
Some common steps in the sterilization cycle of pharmaceutical dry heat sterilizer includes the following
- Pre–Heating Sterilization
- Post – Heating
Let’s look briefly at each of the above stages
Pre-heating is the initial stage when DHS is first started, in which the entire chamber of pharmaceutical dry heat sterilizer is heated to the required temperature. Sensors at each corner monitor the temperature to check for temperature achievement.
Pre-heating is necessary because when personnel loads the DHS with items, different parts of pharmaceutical dry heat sterilizer are at different temperature levels. asa result o fit, some parts of pharma DHS can be easily heated, while others may take longer to achieve the required temperature. Pre – Heating ensures and helps achieve uniform temperature levels throughout the pharma DHS chamber.
Normally, the pre-heating temperature is the same as the sterilization temperature.
When the temperature of the entire chamber becomes equal to the pre-heating temperature, the DHS automatically shifts to the sterilization phase.
The sterilization of pharmaceutical dry heat sterilizer stage starts when the temperature during the pre-heating phase achieves the required temperature. In this stage, the temperature is maintained for a specific time, as defined during the product development stage. During this stage, different sensors at various locations monitor the internal temperature.
When the timer ends, DHS completes the sterilization and moves to the next stage, called Post–Heating.
In the post-heating stage, heating is stopped, and the temperature is lowered. The main purpose of reducing the temperature is to enable easy off-loading. For this purpose, a fan blows the air inside the chamber, while heaters are turned OFF.
When the temperature reaches the acceptable levels defined by the user, the pharma dry heat sterilizer automatically stops, and items can be off-loaded.
Pharmaceutical dry heat sterilizer equipment
Pharmaceutical dry heat sterilizer equipment consists of many sub-components that perform individual functions. Satisfactory working of each component is necessary for the DHS to operate according to specifications.
Some common and critical parts of DHS include but are not limited to, the following.
The Chamber of the pharmaceutical dry heat sterilizer is an enclosed area of stainless steel where items to be sterilized are placed. Chamber also includes a movable trolley, which can move inside and outside the chamber.
The trolley facilitates items placement inside the chamber. For loading the chamber, items are placed on a trolley, and when fully loaded, they are moved inside the pharma dhs chamber
The door is used to close the chamber before starting the sterilization process. There are two configurations of the door – Double Door and Single Door.
In double-door DHS, a loaded trolley enters from one side. After the sterilization process, the trolley is off-loaded from the other side. Both doors cannot be opened simultaneously. For loading, the off-loading door must be closed and vice versa.
In single–door DHS, there is only one door for loading and off-loading items.
Temperature sensors are placed at different locations in the chamber to monitor the temperature during sterilization. Temperature monitoring helps in preventing temperature deviation during the sterilization process.
The heater is used to heat the air flowing inside the chamber. The heater’s heating depends on the chamber’s actual temperature. If the temperature inside the chamber is less than the required value, heaters will continue to generate heat until it reaches the required value.
An air blower is used to blow air inside the chamber. The air from the blower passes through the heaters to become hot. This hot air enters the chamber, increasing its internal temperature and items inside it.
The airflow sensor installed inside DHS controls the air blower’s speed. If the rate of air is less than the required value, the main controller increases the air blower’s speed. Similarly, if airspeed exceeds the required value, the main controller decreases the speed.
Dry heat sterilization temperature sensor
A pharmaceutical dry heat sterilizer uses a temperature sensor to control the sterilization process. It continuously monitors the temperature and sends its value to the main controller for various process requirements. Examples include maintaining temperature during sterilization, monitoring and recording temperature levels, and generating an alarm if the temperature deviates from the standard value
The dry heat sterilization temperature sensor is installed at the coolest point of DHS. Because, the coolest point of dhs is the last to achieve the required temperature, and when the temperature is achieved at the coolest point, every corner, section, and side of DHS has already achieved the temperature, because they are above the coolest point.
Different Temperature sensors are also placed at various locations to monitor real-time temperature values. These sensors help in detecting the fault with the temperature control system.
Pt100, a class of RTD sensors, is used as a dry heat sterilization temperature sensor. This sensor changes its resistance with the increase in temperature. They are capable of withstanding high temperature and pressure of a DHS. PT100 can easily measure the temperature range for which the DHS is designed i.e. from 0 to 250⁰C. Its cable is made up of a material that can easily withstand high temperatures and pressure inside a dry heat sterilizer.
Main Controller and Display System
The main controller contains the program for operating the Dry Heat Sterilizer. It takes input from various sensors such as temperature and airflow. It then uses an algorithm to control different components for a successful sterilization process.
The display system operates the DHS and provides the operator to view different physical parameters. The display is also used to set process parameters such as temperature, sterilization time, and airflow.